Dithieno[3,2-b:2′,3′-d]silole-based low band gap polymers: the effect of fluorine and side chain substituents on photovoltaic performance

Abstract

Three alkyl-thiophene π-bridged polymers, PDTS-hDTFBT (P-hF), PDTS-hDTDFBT (P-hDF) and PDTS-ehDTDFBT (P-ehDF), with different number of F atom and side chain substituents are synthesized through palladium catalyzed Stille coupling reaction. P-hF, P-hDF and P-ehDF show narrow band gap of 1.56, 1.56 and 1.60 eV with deep lying highest-occupied molecular orbital (HOMO) energy levels of -5.17, -5.21 and -5.35 eV, respectively. The optimized P-hDF-based photovoltaic device exhibits an open circuit voltage (VOC) of 0.593 V, a short-circuit current density of 15.98 mA cm -2 , a fill factor of 64.8% and a high energy conversion efficiency of 6.14%, which is partially ascribed to the deep HOMO energy level and good coplanarity. The performance is among the highest reported ones in devices based on polymers with dithieno[3,2-b:2',3'd]silole (DTS) as the electron-rich unit and 2,1,3-benzothiadiazole (BT) derivatives as electron-deficient unit.

A fluorine-induced high-performance narrow bandgap polymer based on thiadiazolo[3,4-c]pyridine for photovoltaic applications

“…[1][2][3][4] During the last decade, remarkable progress has been made in enhancing the power conversion efficiency (PCE) of the PSCs, such as development of high-performance polymer donors, [4][5][6][7][8][9][10][11][12][13][14] incorporation of efficient interfacial materials, [15][16][17] and advancement of device architectures. [1][2][3][4] During the last decade, remarkable progress has been made in enhancing the power conversion efficiency (PCE) of the PSCs, such as development of high-performance polymer donors, [4][5][6][7][8][9][10][11][12][13][14] incorporation of efficient interfacial materials, [15][16][17] and advancement of device architectures.…”

The effect of tuning chemical structure on the open‐circuit voltage and photovoltaic performance of narrow band‐gap polymers

“…Meanwhile, it was reasonable that P3 exhibited the highest J sc among these three polymers because of the good charge transport ability. Furthermore, the low hole mobility of P2 might be caused by the decreased planarity of the backbone and poor crystallinity …”

“…They were −3.31, −3.64, and −3.38 eV for P1, P2, and P3, respectively. And the LUMO differences between these polymers and PC 71 BM were large enough to overcome the exciton binding energy and guarantee efficient exciton dissociation and transfer …”

“…Thus, a higher J sc should be expected for P1‐ and P3‐based PSCs due to the broad absorption. The larger optical band gap of P2 might be ascribed to the tortuous polymer backbone which was caused by the steric hindrance . In addition, all of these polymers showed small red shift from solution to thin film, and strong aggregation of polymer itself was supposed in the solution.…”

“…Owing to the effect of branched side chains, P2 showed a deeper HOMO level of −5.35 eV which was conductive to obtain high V oc . Generally, it was considered that the deeper HOMO level was aroused by the steric hindrance . As shown in Supporting Information Figure S3, the introduction of branched side chains indeed brought some steric hindrance.…”